This application relates to ultrasonic surgical systems and, more particularly, to switch members having membrane seals which prevent gas and water vapor from contacting switch assemblies which are disposed within an internal switch chamber formed in a surgical handpiece.
It is known that electric scalpels and lasers can be used as surgical instruments to perform the dual function of simultaneously effecting the incision and hemostatis of soft tissue by cauterizing tissues and blood vessels. However, such instruments employ very high temperatures to achieve coagulation, causing vaporization and fumes as well as splattering. Additionally, the use of such instruments often results in relatively wide zones of thermal tissue damage.
Cutting and cauterizing of tissue by means of surgical instruments, e.g., blades, vibrated at high speeds by ultrasonic drive mechanisms is also known. In such systems, an ultrasonic generator is provided which produces an electrical signal of a particular voltage, current and frequency, e.g., 55,500 cycles per second. The generator is connected by a cable to a handpiece, which contains piezoceramic elements forming an ultrasonic transducer. In response to a switch on the handpiece or a foot switch connected to the generator by another cable, the generator signal is applied to the transducer, which causes a longitudinal vibration of its elements. A structure connects the transducer to a surgical blade, which is thus vibrated at ultrasonic frequencies when the generator signal is applied to the transducer. The structure is designed to resonate at the selected frequency, thus amplifying the motion initiated by the transducer.
In order to activate the handpiece so that the blade is vibrated or otherwise operated, a switch mechanism is manipulated by the user. The switch mechanism typically includes one or more switch button members which the user depresses to cause activation of the blade. Because it is necessary for the handpiece to be cleaned and/or serviced after use, the internal electronic components of the switch mechanism must be sealed from the environment outside of the handpiece to prevent damage to the electronic components during the cleaning, use, handling, or servicing thereof. This is particularly true for handpieces which are autoclavable and/or immersible. Consequently, a membrane (e.g., a flexible seal) may be included as part of the switch member for sealing the electronic components of the switch mechanism so that the handpiece may be cleaned and/or serviced without having the electronic components damaged.
Typically, the switch member (having button portions) is formed of a resilient material, such as an elastomeric material, to provide a sealing action between the switch member and the handpiece. Elastomeric switch buttons are generally not good barriers to moisture ingress (water vapor), especially moisture ingress due to an autoclave operation. Elastomeric materials are vulnerable to piercing by sharp instruments. Also, if moisture does pass through these elastomeric barriers during the autoclave operation, the moisture does not have a rapid means for escaping the handpiece following completion of the autoclave operation. The presence of moisture in an inner cavity of the handpiece, where the electronic components are stored, can cause damage and/or malfunction of the handpiece or lead to premature wear.
When the switch member is in the form of an elastomeric switch member, an integral flexible membrane may be provided around the periphery thereof. This flexible membrane is often referred to as a xe2x80x9cwebxe2x80x9d or skirt which permits the switch member body to be readily depressed when pressed upon and return to its original position when released. There are at least two associated disadvantages of using a thin elastomeric web as part of the rocker switch member body. First, the puncture/tear resistance of the web area is limited because the web area has a relatively thin cross section and has limited durability to resist puncture from sharp instruments contacting the flexing portion (the web). Second, the thinness of the web membrane does not provide a very robust seal since air and humidity can pass through. In other words, the web membrane has a sufficiently high permeability that permits air and humidity to pass through.
One example of the difficulty that is encountered with a switch member having a high permeability occurs when the switch member is subjected to an autoclaving process. When the rocker switch member is used to seal off an inner cavity of the handpiece, an autoclave vacuum can cause the air pressure inside the inner cavity to be higher than outside of the inner cavity. The switch member has limited travel in an outward direction and thus can not accommodate the higher pressure. Consequently, the pressurized air escapes through the web membrane due to its relatively poor permeability. It is also possibly that the pressurized air can escape through other portions of the switch member body. However, during autoclave repressurization to normal atmosphere, the reduced pressure inside the inner cavity causes the switch member to deflect downward. This results in the switch member being pulled downward, similar to someone pressing on the switch member. Thus, the switch member equalizes the pressure and there is inadequate pressure differential to draw air back through the web membrane. This results in the switch member being held down without user intervention. This is not desirable because it leads to unwanted activation of the switch mechanism due to the switch member being in a depressed position.
While existing membranes have been suitable for some applications, there is a need for providing improved membranes which are good barriers to moisture ingress along with providing a good barrier to gas vapor and other gas (air) transmission along with improved resistance to puncture.
The present application is directed toward methods and switch members which control fluid flow (e.g., flow of water vapor and gases, such as air) through the switch members which are used to seal an interior cavity of a surgical handpiece and each provides a depressable member for actuating the handpiece. The switch members provide improved sealing properties which prevent transmission of fluids across the entire switch member or at least a treated portion thereof (e.g., a skirt) and into and out of the sealed internal switch chamber. The switch members are also resistant to puncture due to striking by tools or cleaning instruments, and the like.
The switch members find particularly utility in handpieces which are autoclavable. Autoclave pressures and vacuums can induce gas flow and water vapor flow across the membranes of conventional switch members and particularly, across the thin skirt portion thereof. The present application discloses various methods of controlling the gas and water vapor flow across the depressable switch member (particularly the skirt portion) such that the handpiece may be used in an autoclave environment and other adverse settings without experiencing the disadvantages associated with conventional members.
Other features and advantages will be apparent from the following detailed description when read in conjunction with the accompanying drawings.